I’ve got no experience with nixos (so YMMV), but I do run libvirt . Is virt-manager available in your install and if so what happens when you try to run virt-manager from the command line? IIRC I deployed my Win11 VM straight from the virt-manager gui and didn’t need to touch any of the config files
Had a similar issue with tlp recently. I just happened to notice the laptop battery was at 100%, and said it was charging. I double and triple checked the config file, but the tlp-stat -b still showed the thresholds at 90%-100%.
Turns out tlp, at some point, started ignoring /etc/tlp.conf, and was pointing to /etc/default/tlp